In communication systems, signals are sent in packet form from a first communication node through a network to a second communication node. The first and second communication nodes may implemented in any number of ways, including but not limited to as a wireless base station, a wireless access point (AP), computers such as a server computer, a personal computer, a laptop, a personal digital assistant (PDA), a smart phone, a hand-held computing device (e.g., a personal digital assistant (PDA)), a mobile telephone, a media playing device, a portable gaming device, a personal computer, a laptop computer, another suitable wireless communication device, or any combination thereof.
These packets typically include one or more headers and a payload, which is the useful data to be sent, received and used by the communication nodes. The signals generated by the first communication node may reach the second communication node via a number of different channels, the characteristics of which typically change over time due to the phenomena of multi-path and fading. Moreover, the characteristics of a channel differ or vary based on the frequency of propagation. To compensate for the variations and to enhance effective encoding and modulation in the communication system, each communication node of the communication system may periodically develop or collect channel state information (CSI) for each of the channels. Generally speaking, CSI is information defining or describing one or more characteristics about each of the channels. Upon determining the CSI for one or more channels, the communication nodes may send this CSI back to the transmitter, which may use the CSI for each channel to precondition the signals transmitted using that channel so as to compensate for the varying propagation effects of each of the channels.